Currently, most adhesives generally used in adhesive tapes, labels and the like are solvent type adhesives and discharge volatile organic compounds (VOCs). Thus, recently, development from solvent type adhesives to aqueous adhesives has been made to satisfy tightened environmental regulations.
Techniques related to an aqueous adhesive composition are disclosed in documents, such as Korean Patent Publication No. 10-017741 and the like. An aqueous adhesive prepared through emulsion polymerization in the art typically uses acrylic acid as a functional monomer in order to impart high peel strength and cohesion. Use of acrylic acid in the aqueous adhesive composition enables impartment of high adhesion regardless of types of adherends. However, such acrylic acid reacts with ionic impurities included in initiators, emulsifiers, neutralizers and thickeners to form a chelate after polymerization. Such a chelate increases gel content, causing increase in hardness and reduction in adhesion of adhesives.
As described above, to prevent formation of the chelate due to the acrylic acid and ionic impurities, low-ionic emulsion polymerization may be performed. However, emulsion polymerization using a minimum amount of nonionic chemicals has a problem of deterioration in productivity due to deterioration in polymerization stability and generation of agglomerates. In addition, there is a problem in that defects are generated in a finally prepared adhesive coating layer.
To solve such problems, there is a need for an aqueous adhesive composition which is not affected by ionic impurities used in emulsion polymerization.